Method for Making Wavelength-Selective, Integrated Resonance Detector for Electromagnetic Radiation

ABSTRACT

Embodiments of the invention are directed to integrated resonance detectors and arrays of integrated resonance detectors and to methods for making and using the integrated resonance detectors and arrays. Integrated resonance detectors comprise a substrate, a conducting mirror layer, an active layer, and a patterned conducting layer. Electromagnetic radiation is detected by transducing a specific resonance-induced field enhancement in the active layer to a detection current that is proportional to the incident irradiance.

This is a continuation application and claims priority to U.S.application Ser. No. 13/329,503 filed on Dec. 19, 2011.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

The invention was supported, in whole or in part, by contractsW31P4Q-09-C-0512 “Nonlinear Plasmonic Devices” from the Defense AdvancedResearch Projects Agency (DARPA) and FA9550-10-C-0003 “PonderomotiveField Effect Transistor” from the Air Force Office of ScientificResearch, and N00014-09-M-0292 “Electromagnetic Metamaterial Films” fromthe Office of Naval Research (ONR). The U.S. Government has certainrights in the invention.

FIELD OF THE INVENTION

The present invention relates to the field of wavelength-selectivedetectors and arrays. More specifically, the invention relates tomethods for making and using devices with subwavelength structureshaving wavelength-selective properties that are integrated with adetector for electromagnetic radiation detection, and the ability tomake such devices into a flexible format.

BACKGROUND OF THE INVENTION

Over the past fifty years, technological advancements inmicroelectronics and microelectro-optics have proceeded at a rapid pace.As a result of this success, today's microfabricated devices and sensorsare inexpensive, can be produced in large volumes, and can be fabricatedwith billions of sub-100 nm logic elements as small area microchips. Onestrong candidate for continued miniaturization is the integration ofoptical detectors with electronics for both logic processing andelectromagnetic radiation detection (Kobrinsky, M., “On-chip opticalinterconnects” Intel Technology, 2004. 8, p. 129 and Ozbay, E.,“Plasmonics: Merging photonics and electronics at nanoscale dimensions”Science, 2006, 311, p. 189). Optical signals offer an almost unlimitedbandwidth and low loss, and therefore, it is highly desirable to coupleoptics and electronics at the wafer or device level to develop novelarchitectures. Pat. App. WO 2011/050272 A3 discloses nanoantenna arrayscomprising plasmonic nanostructures or non-plasmonic nanostructures.

The inventors have realized a need for a detector that is integratedwith a wavelength-selective element that can detect numerous narrowspectral regions over a broad region of the electromagnetic spectrumfrom ultraviolet to long wave infrared. Such a device can eliminate theexisting requirement for multiple detectors and bulkywavelength-selective detection systems, which are expensive, large, andrequire high power levels to operate. A detector that provides thiscapability is not known in the art.

An array of integrated wavelength-selective detector devices, eachhaving a sub-wavelength structure specific to a particular narrow bandof wavelengths, can provide a means to detect a broad range ofwavelengths for purposes of multi-spectral imaging. Such a method canprovide a means to transduce multi-spectral responses from theultraviolet, visible, infrared, and microwave regions of theelectromagnetic spectrum using a single detector array structure. Amethod to control the feature dimensions of the sub-wavelength structurecan provide a means to readily tune the device structure to interactwith a wide range of specific wavelengths. Furthermore, methods formaking the integrated wavelength-selective detector into large areadetector arrays that are not subject to limitations imposed by singlecrystal substrates (i.e., inherently flexible or conformable substratesthat can lead to curved detector geometries) can be advantageous. Such adevice can benefit from the large bandwidth of signals that could bedelivered directly from a fiber optic, or from broad wavelength-band(spectral) imagery, e.g., imaging applications such as hyperspectralimaging. Furthermore, large area detectors, with some level ofconformability or flexibility, can open new applications in imaging suchas device integration into textiles and other fabric material for covertsurveillance. Monolithic detectors for broadband electromagneticradiation detection can simplify and reduce the size, weight and powerrequirements for multiple mechanical systems required to achieve multi-and hyperspectral imaging today.

SUMMARY OF THE INVENTION

The inventors have developed a method for fabricating arrays ofdetectors with integrated wavelength-selective components. Embodimentsof the invention provide a means for the assembly of a broad range oftunable detector structures precisely defined to resonantly couple withspecific wavelengths of electromagnetic radiation. Each unique detectorstructure is electrically addressable such that resonantly-coupledelectromagnetic radiation is transduced into a quantifiable electriccurrent proportional to the incident power density in that specificspectral region.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings form part of the present specification and areincluded to further demonstrate certain aspects of the presentinvention. The invention may be better understood by reference to one ormore of these drawings in combination with the detailed description ofspecific embodiments presented herein.

FIG. 1 is a flow chart diagram depicting the method for making anintegrated resonance detector.

FIG. 2 shows a cross section view of an integrated resonance detectorwith current measurement across the structure.

FIGS. 3A, 3B, 3C, 3D and 3E are schematic representations of an array ofintegrated resonance detectors.

FIG. 4 is a cross section diagram of an array of integrated resonancedetectors responding to different wavelengths of electromagneticradiation.

FIG. 5 is a schematic representation of the embodiment comprising abilayer active layer.

FIG. 6 is a schematic representation of the embodiment comprising acomposite active layer with two materials.

FIG. 7 is a diagram of an array of integrated resonance detectorsdepicting a thin layer that forms an array of patterned conductorfeatures that are electrically contiguous, but does not interfere withresonance absorption.

FIG. 8 is a schematic diagram illustrating an array of integratedresonance detectors in which an integrated resonance detector isinterdispersed within the photosensitive elements of a CMOS image sensorbearing a color filter array.

FIG. 9 is a photograph illustrating a wafer device structure withdetails of an integrated resonance detector.

FIG. 10 is a plot illustrating the change in peak resonance absorptionbased on the feature dimensions of the patterned conductor layer of theintegrated resonance detector.

FIG. 11 is a photograph illustrating fabrication of an array ofintegrated resonance detectors onto a flexible Kapton® substrate.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention are directed to ultraviolet, visible, andinfrared photodetector arrays and methods for fabricating and usingintegrated resonance detectors, and arrays made thereof, for wide-angle,multi- and hyperspectral imaging. In certain aspects, devices andmethods of the invention are useful for spectroscopic detection ofelectromagnetic radiation in the ultraviolet, visible, near infrared(NIR), short-wave infrared (SWIR), mid-wave infrared (MWIR), andlong-wave, or far infrared (LWIR), or millimeter-wave, or microwave orcombinations of these. Integrated resonance detector arrays of theinvention enable narrow wavelength selection and the generation ofelectric current that does not depend on the absorptivity of a specificwavelength region by the detector material. Structural features ofdetectors of the invention can be lithographically patterned such that aresonance condition with sufficient field enhancement in the activelayer produces measurable changes in electric current when illuminatedwith electromagnetic radiation that is in resonance with the structure.

Referring to FIG. 1, the method for fabricating an integrated resonancedetector is illustrated. In this example, a substrate is supplied instep 101. The substrate may be a semiconductor wafer a ceramic plate oralternatively, the substrate may be a glass or another “transparent”plate that is non-interacting with the full range of spectral bandpassof the integrated resonance detector. The substrate need not be a rigidmaterial such as a wafer or plate; rather, it may be a flexiblematerial, such as a metal foil with a mirror finish, a polymer or otheramorphous sheet with a metal mirror layer deposited on the surface usingtechniques known in the art, such as evaporation, vapor deposition,plasma deposition, vacuum deposition, sputter deposition or electrolessdeposition. A number of possible flexible substrates are known in theart that could be used to fabricate the integrated resonance detectorincluding metal, ceramic, plastic or biomaterials.

In some embodiments, the substrate may consist of a singlephotodetector, a linear photodetector, or a photodetector array such asa commercial image sensor or focal plane array. Portions of thephotodetector array may be modified to accommodate additional detectorelements fabricated by methods of the invention. The substrate may alsobe a portion of a wafer containing pre-fabricated electronic circuitsthat may or may not be associated with integrated resonance detectors.

The area of the conducting mirror layer generally defines the area foran integrated resonance detector. For arrays of integrated resonancedetectors, the conducting mirror layer for each integrated resonancedetector may be non-contiguous with neighboring integrated resonancedetectors in the array. Arrays of electrically isolated conductingmirror layer that form isolated electrodes can be connected toindividually addressable electronic circuits that may be present in thesubstrate.

Numerous methods are known in the art for depositing the active layer(step 102) comprising dielectric, semi-insulating, or semiconductormaterials in the structure, including vacuum deposition and spin-on, orcasting methods. In one embodiment, the active layer comprises a singlecomposition such as doped-Si, or environmentally-stable semiconductorse.g. metal oxides such as ZnO, In₂O₃ or SnO₂. In other embodiments, theactive layer includes a bilayer, or multilayer structure which mayinclude insulating barrier layers such as SiO₂ which can reduce darkcurrent by acting as a tunnel barrier. In other embodiments, the activelayer may be a composite mixture of materials that can affect thenonlinearity of the electric-field-induced current, for example,semiconducting nanoparticles mixed with a bulk insulating material thatleads to variable range hopping current.

Following deposition of the active layer in step 102, a conducting layeris deposited and patterned with the desired feature dimensions forabsorption of a specific wavelength range, in step 103. Typicaldimensions of features of the patterned conducting layer correspondingto absorption in the short wave infrared band are on the order ofhundreds of nanometer linewidths with tens to a few hundreds ofnanometer gaps. The composition, lateral dimensions, and thickness ofthe patterned conductor layer together with the active layer thicknessdefine the “resonance structure” that determines the resonancewavelength. The degree of wavelength specificity, or Q factor, isdefined by controlling the materials, their dimensions, and thesharpness of the features. The patterned conductor layer is connected toa common electrode and the conducting mirror layer is connected to aseparate electrode, in step 104. A bias voltage applied between theconducting mirror layer and the patterned conductor layer provides anelectric field in the active layer, which in some cases causes a “darkcurrent” in the absence of radiation that illuminates the detector. Incertain embodiments, this current is low, or effectively zero. Whenresonance absorption conditions are met by incident externalelectromagnetic radiation, field enhancement in the active layer causesadditional charge carriers to form and flow between the patternedconducting layer and the conducting mirror layer. The salient feature ofthe active layer is that it has nonlinearity in its current vs. voltagecharacteristic at the applied bias voltage. The purpose of the appliedbias voltage is to maximize the amount of this nonlinearity. The activelayer nonlinearity causes an asymmetry in theelectromagnetic-wave-induced current oscillations in the active layer,which is subsequently measurable as a change in the time-integratedcurrent. The nonlinearity in the current vs. voltage characteristic ofthe active layer rectifies the current induced by the incidentelectromagnetic radiation. The change in rectified current from “dark”to “illuminated” conditions provides a quantifiable indication of theirradiance of the selectively absorbed radiation.

In embodiments of the invention, the resonance structure is specificallydesigned to select a spectral band of electromagnetic radiation. Thespectral band is not limited to any particular region of theelectromagnetic spectrum, provided that suitable feature dimensions ofthe resonance structure are fabricated using high-definition patterningsuch as nanoimprint lithography (i.e., the smallest feature requirementbeing in the 10s of nanometers for ultraviolet absorption and thelargest being in the millimeter range for microwave radiation).Likewise, the device response is not dependent on the absorptivity orband structure of a specific substrate material, rather, the incidentradiation is transduced into an electric current in the active layer.Resonance structures that include two or more feature dimensions may beused to absorb multiple wavelengths. Amorphous materials that aredeposited by evaporation, chemical vapor deposition, sputter-deposited,plasma-deposited, or spun-on are preferred for flexible substrates forintegrated resonance detectors. The ability to fabricate integratedresonance detectors with high sensitivity and tunable wavelengthselectivity on a flexible substrate is one of the unique features of theinvention and is not known in the art.

FIG. 2 illustrates a cross-sectional view of one embodiment of anintegrated resonance detector 220. Substrate 201 is first supplied.Substrate 201 may be either rigid (e.g., a plate or wafer), or flexible(e.g., a metal foil, or metallized film) and may comprise a number ofsingular materials such as plastic, ceramic, metal, glass, orsemiconductor or a composite mixture of any two or more components.Depending on the substrate material, transparency to a particularspectral range may be enabled such that illumination of the detectorscan be made either from the top of the structures, or through substrate201. In the case of a transparent substrate 201, it may be advantageousto fabricate the individual layers of the integrated resonance detectorin reverse order. Conducting mirror layer 202 is deposited on substrate201 and active layer 203 is deposited onto conducting mirror layer 202.Conducting mirror layer 202 may be contiguous, or alternately, may bemacroscopically patterned to electrically isolate regions of the devicefor the purposes of making each detector independently addressable in anarray. Conducting mirror layer 202 may comprise any reflectiveconducting material including, but not limited to, noble metals orrefractory metals. Active layer 203 may comprise numerous compositions,for example amorphous semiconductors, homogeneous mixtures of differentcompounds, alloys, inhomogeneous mixtures of nanomaterials, porousfilms, allotropic mixtures, or bilayer or multilayer stacks. Bilayer ormultilayer stacks may include rectifying junctions such as diodes. Theselection of the composition and thickness of the active layer is basedon maximizing the nonlinearity in the current vs. voltage characteristicthrough the thickness of the active layer. Patterned conductor layer 204is then deposited and patterned atop active layer 203. Patternedconductor layer 204 is generally metallic; however, the composition needonly meet the requirements of resonance coupling and electricalconductivity to support a desired response to incident radiation.Subsequently, patterned conductor layer 204 is processed to formpatterned features 205. Fabrication of patterned conductor layer 204 canbe carried out using lithographic techniques, which may includenanoimprint lithography to achieve features small enough to supportresonance coupling in the ultraviolet through SWIR regions.

In the diagram of FIG. 2, individual patterned features 205, inpatterned conductor layer 204, are illustrated with a specific featurewidth 206 and pattern pitch 207. In certain embodiments, individualpatterned features 205 are created by etching the full thickness 208 ofpatterned conductor layer 204 leaving a periodic series of electricallyunconnected (isolated) patterned features 205. However, the etchedthickness of patterned features 205 need not extend the full thickness208 of patterned conductor layer 204, such as in the case when it isdesirable to have a residual conducting plane for purposes ofelectrically connecting an array of features 205 (illustrated further inFIG. 7). In the case where the patterned features 205 are an array oflines, electrical continuity between all patterned features 205 inpatterned conductor layer 204 can be provided with a bridging strip ofconducting material 209. Bridging strip 209 may be part of the pattern,as depicted here, or may occur in a post-processing step. Placement ofbridging strip 209 at one edge of patterned features 205 provides ameans for all of the patterned features 205 of patterned conductor layer204 to be electrically connected, but not interfere with the resonancecoupling of electromagnetic radiation. A wide variety of techniques fordepositing, patterning, etching, forming, and creating specificstructures of integrated resonance detector 220 are known in the art.Operation of the novel integrated resonance detectors described here isnot sensitive to the techniques used for fabrication, as long as thematerial characteristics and dimensions of the layers comprising thedevice are achieved and maintained across the lateral extent of thedevice.

The electrical conductivity of conducting mirror layer 202, thethickness of active layer 203, the thickness of patterned conductorlayer 204, and the dimensions of the patterned features 205 of patternedconductor layer 204 are designed to selectively interact with, or absorbspecific wavelengths of electromagnetic radiation 210. Together, theselayers and their specific dimensions form the resonance structure 219.Upon absorption of radiation 210, resonance-induced field enhancement,represented by electric field lines 211, occurs between patternedconductor layer 204 and conducting mirror layer 202. Nonlinearity in theactive layer 203 and the electric field enhancement 211 causes a netelectric current 212 to flow to current measurement device 218, which ispart of an electronic circuit connected to the resonance structure. Insome cases an external voltage bias from an electromotive source 213 inthe electronic circuit is applied across patterned conductor layer 204and conducting mirror layer 202 to maximize the nonlinearcharacteristics of the active layer 203. Net current 212 is the resultof the nonlinear rectification of the alternating electric field ofelectromagnetic radiation 210 during resonance coupling, and is thedifference between the collective forward currents 214 and reversecurrents 215, integrated over the lateral dimensions of the device. Theelectric current 212 is coupled to the external electric circuit fromconducting mirror layer 202 through electrode terminus 216 on one sideand through electrode terminus 217 on the other side which terminates atbridging strip 209. Bridging strip 209 is common to all the patternedfeatures 205 of patterned conductor layer 204 making the whole layer acontiguous conductor. The magnitude of electric current 212 is measuredusing external current measuring device 218. The magnitude of electriccurrent 212 for a given exposure interval can be used to determine theincident irradiance of electromagnetic radiation 210 incident on thedetector surface, which could be a transistor amplifier such as a focalplane array, image sensor, bolometer or other electronics, such as thatpertaining to, for example, photodetector arrays. Wavelength-selective,integrated detector structures provide a means for direct opticaldetection, across a wide spectral region, in a large area, flexibledevice format. Such a format would enable a detector that couldaccommodate parabolic geometries similar to the human eye.

In embodiments of the invention, efficient detection ofwavelength-selective components of broadband electromagnetic radiation210 is realized by the direct detection of resonantly absorbedradiation. This is superior to methods that employ external wavelengthfiltering elements. Conversely, nanoimprint lithography of integratedresonance detectors 220 enables the fabrication of a conducting mirrorlayer 202, active layer 203, and patterned conductor layer 204 tosimultaneously serve as both the resonance coupler and transducer,thereby removing the requirement for a separate absorbing, or filteringlayer.

In embodiments of the invention, the maximum detector current isobtained when incident electromagnetic radiation 210 is in resonancewith the peak of the absorption curve for an integrated resonancedetector 220 and therefore generates the largest field enhancement inactive layer 203. Electromagnetic radiation 210 that is not in resonancewith the structure does not result in electric field enhancement, andonly the background current is measured. The background current isestablished for each integrated resonance detector 220 and is very smallin most structure embodiments, such that the largest differentialresponse is obtained during on-resonance illumination for a givenintegrated resonance detector 220. The electric field strength in activelayer 203 is thus proportional to the incident field and also to thedegree to which resonance occurs in the structure, the resonantbandwidth determined by the sharpness or Q-factor of the structure. TheQ-factor is dependent, in turn, upon feature dimensions 205, the spatialvariation of the dimensions, and the fabrication details of the device.

The specific resonance wavelength(s) for a given integrated resonancedetector 220 depends on the size of the features 206 (i.e., 10 nm to 1μm) in patterned conductor layer 204, the spacing of the features 207(30 nm to 20 μm), the gap between features (10 nm to 20 μm), thethickness 208 of the features in patterned conductor layer 204 (1 nm to1 μm), the buried conducting mirror reflectance, the active layerthickness (0.3 nm to 500 nm), and the properties of any other materialthat might be present in regions between features, and on the surfaceroughness of patterned conductor layer 204.

FIGS. 3A, 3B, 3C, 3D and 3E are schematic representations of an array ofintegrated resonance detectors. FIG. 3A shows substrate 201, upon whicha 2×2 array of integrated resonance detectors 220A-D are to befabricated represented by segmented regions 301A-D. Substrate 201 maycomprise a conventional photodiode detector array that the integratedresonance detectors 220A-D may be fabricated upon. Substrate 201 may bedesigned such that all of the photosensitive elements thereon areintegrated resonance detectors 220, or some fraction of the detectorsare integrated resonance detectors 220 with the rest composed ofphotodiode detectors such as silicon photodiodes. For example, a siliconCMOS image sensor may be provided as substrate 201 with its associatedread out electronics for each photodiode. A subset of the read outelectronics may be directed to connect with integrated resonancedetectors 220 that may be patterned and assembled in the methodillustrated in FIG. 3. Integrated resonance detectors 220 incorporatedinto existing CMOS photodetector arrays may add functionality such asinfrared detection to an existing CMOS device.

In another embodiment, substrate 201 may wholly comprise a material withspecial optical, mechanical, or electrical characteristics such as aglass slide for optical transparency. In still another embodiment,substrate 201 may comprise a large area polymer film. The polymer filmmay provide a means for making large area sheets of integrated resonancedetector arrays using low cost roll-to-roll manufacturing methods. Inthe embodiment where integrated resonance detectors 220 are depositeddirectly on a polymer film, patterned electrodes, may be present on theentire array surface or on selected regions of the surface of substrate201 where the integrated resonance detector 220 array is formed.

The two electrode terminals, 216 for conducting mirror layer 202 and 217for patterned conductor layer 204, respectively, for each of the four(2×2) segmented regions 301A-D that will be used to fabricate fourintegrated resonance detectors 220A-D are also depicted in FIG. 3A. Thecontacts are depicted as buried leads interfacing to some circuitry notvisible in the figure. In practice, numerous methods exist in the artfor fabricating electrical interconnects and electrode contacts orterminals that provide connectivity to the read out electronics forindividual elements in the array.

FIG. 3B shows distinct, arrayed conducting mirror layer segments 202A-Ddeposited onto the four segmented regions 301A-D of substrate 201.Deposition is carried out such that each conducting mirror layer 202A-Dmakes electrical contact with its respective electrode terminal 216A-D.The electrical connection occurs beneath conducting mirror layer 202A-Dand is not visible in the figure. In this embodiment, the remainingpatterned conductor layer terminals 217A-D are left exposed, or areetched back to form a via, or throughhole, using lithographic processes.Deposition of conducting mirror layers 202A-D is followed by depositionof active layers 203A-D, FIG. 3C. Active layer 203 may consist of anumber of materials with electrical properties ranging from insulating,semi-insulating, and semi-conducting and may include bilayer, trilayer,or multilayer structures in order to derive the properties necessary forfield enhancement-induced current generation. Depending on thecomposition of active layer 203, numerous methods for deposition may beemployed. Like deposition of conducting mirror layer 202, active layer203 is generally not deposited over electrode terminals 217A-D. FIG. 3Dillustrates the deposition and lithographic processing of patternedconductor layer 204A-D over active layer 203A-D. Generally, this layercompletes the resonance structures 219 that results in the formation ofintegrated resonance detectors 220A-D. Patterned conductor layer 204 canbe deposited using various deposition techniques described previouslyfor conducting mirror layer 202. In some embodiments, patternedconductor layer 204 is the same composition as conducting mirror layer202, but this is not a requirement. Numerous metal options are usefulincluding high temperature metals and refractory metals such as tungstenand molybdenum for applications such as thermophotovoltaic devices.

Lithographic processing of patterned conductor layer 204A-D is carriedout using methods that can achieve the necessary feature dimensions.Long wave infrared devices will have large feature dimensions that arereadily attainable with standard lithography methods well known in theart. If feature dimensions commensurate with short wave infraredradiation, near-IR, or visible are desired, then lithographic techniquesthat can create nanoscale features are necessary. The figure illustratesdifferent sizes and pitches for each segmented region 301A-D that areformed in patterned conductor layer 204A-D. In some embodiments,nanoimprint lithography (NIL) is a useful method for creating nanoscalefeatures. NIL provides a means for making integrated resonance detectorsthat are useful for detecting radiation having short wavelengths.Similarly, methods of roll-to-roll nanoimprint lithography, such as byway of example only, those described by Guo, L. et al., U.S. PatentAppn. No. 2009/0046362, which is hereby incorporated by reference, maybe used to manufacture arrays of integrated resonance detectors 220.

In FIG. 3D, the set of four (2×2) integrated resonance detectors 220A-Dare illustrated. A final connection between patterned conductor layer204A-D and patterned conductor electrode terminals 217A-D is made. Thiscan be performed by a number of different methods well known in the art,including the use of bridging strip 209 depicted previously in FIG. 2.This step is not illustrated in FIG. 3D for clarity. Electricalconnection of integrated resonance detectors 220A-D to the underlyingelectrical circuit below segmented regions 301A-D results in theformation of a 2×2 array of integrated resonance detectors 220A-D whichin this figure represent a “unit cell” 302 of a larger integratedresonance detector array depicted in FIG. 3E.

In some applications, as illustrated in FIG. 3E, numerous unit cells302A-N can be repeated across substrate 201 to form a large array 303 ofintegrated resonance detectors. An embodiment of large array 303 wouldconsist of a multiple unit cells 302 fabricated on a plate or flexibleroll substrate 201, and need not include regular spacings of integratedresonance detectors 220. In another embodiment, large array 303 maycomprise an entire array of unique integrated resonance detectors 220 inany number of positional assemblies. Using lithographic processes suchas NIL, the patterning of the patterned conductor layer 204 for allelements of the entire large array 303 of integrated resonance detectorscan be fabricated during a single imprint transfer process.

The substrate 201 for an array of integrated resonance detectors 220 maybe an array of electric circuits of an image sensor or focal plane arrayin which integrated resonance detectors 220 are registered to specificareas in the substrate, overall forming a photodetector. In someinstances, the photodetector may be a hybrid that includes traditionalsilicon photodetectors mixed with integrated resonance detectors 220 ofthe present invention. In other aspects of the invention, the detectormay be a silicon, InGaAs, InSb, or HgCdTe focal plane array or imagesensor that includes spectral filter mosaic layer elements replaced withintegrated resonance detectors 220 in such a fashion that electricaladdressability is maintained with the underlying photodetector circuitelements.

A large array 303 of integrated resonance detectors 220 that has beendesigned with different sets of feature dimensions so as to interactwith a selected range of wavelengths of electromagnetic radiation isillustrated in the cross-sectional diagram in FIG. 4. Broadbandelectromagnetic radiation 401 is incident on large array 303. In FIG. 4,three different wavelengths of electromagnetic radiation represented by210A-C are shown at the bottom of broadband electromagnetic radiation401 and are meant to illustrate that specific wavelengths are absorbedonly by the respective integrated resonance detector 220 with thecorrect feature dimensions for resonance with that wavelength (Aspecific example is illustrated later in FIG. 9). In practice, broadbandelectromagnetic radiation 401 impinges on all of the integratedresonance detectors 220 in the array, but only radiation 210 matchingthe conditions for resonance, in any given detector 220, is absorbed.Unabsorbed radiation is either reflected by conducting mirror layer 202or passes through integrated resonance detector 220.

The cross-sectional diagram of FIG. 4 illustrates three uniqueintegrated resonance detectors 220A-C. The feature dimensions 205A-C ofpatterned conductor layer 204A-C and their thicknesses 208A-C and thethicknesses of the active layers 203A-C serve to spectroscopically“filter” or “absorb” electromagnetic radiation by virtue of “resonance”with a specific narrow set of wavelengths 210A-C, respectively, frombroad spectrum radiation 401. The feature width 206A and feature pitch207A of patterned conductor layer 204A are larger than the correspondingfeature width 206B and feature pitch 207B which are, in turn, largerthan the feature width 206C and pitch 207C in this illustration. Thisprogression of feature dimensions 205A-C is represented in FIG. 4. As anexample, FIG. 4 indicates an embodiment where feature dimensions 205Amay be sized to interact with short wave infrared radiation (SWIR) 210A,the feature dimensions 205B are sized to interact with near infraredradiation (NIR) 210B, and the feature dimensions 205C are sized tointeract with visible radiation (VIS) 210C regions of electromagneticradiation. Similarly, all three feature dimensions 205A-C may be sizedto resonate with narrow but distinct spectral regions in any givenspectral band. In embodiments of the invention, the degree ofinteraction is defined by the feature dimensions 205 and materialcomposition which are selected for the desired application. In aspectsof the invention, detectors and methods for detecting can be broadlyapplied to any portion of the electromagnetic spectrum provided thatpatterned conductor layer 204 is patterned with feature dimensions 205that are selected for interaction with the desired radiation range.

FIG. 5 shows an embodiment of integrated resonance detector 220 whereactive layer 203 is composed of a bilayer structure. In the example, themajority composition 501 of active layer 203 may be a semiconductor or amaterial with relatively high electrical conductivity that supplies alarge number of charge carriers. A secondary layer 502 such as a thinsemi-insulating or insulating barrier layer may be provided that servesas a potential barrier or tunnel junction. Barrier layer 502 may providean initial barrier to electric current flow, but may begin conductionunder sufficient electric field achieved via electric field enhancement211, thereby enabling the flow of net electric current 212. In thisillustration, only a select few electric field lines 211 are presentedfor clarity to show the regions of highest electric field strength andthe relationship to the geometry of patterned conductor layer 204. Whenthe optical resonance conditions are met, i.e., when integratedresonance detector 220 absorbs the specific wavelength ofelectromagnetic radiation intended by resonance feature dimensions 205,electric current 212 will flow between patterned conductor layer 204 andconducting mirror layer 202 through active layer 203 via electrodeterminals 216 and 217, to be quantified in external circuit 218. In thisembodiment, barrier layer 502 can be thought of as a nonlinearelectric-field-actuated switch which provides a means to suppressbackground or dark current when either no radiation or off-resonanceradiation is incident on integrated resonance detector 220. Whenresonance conditions are met, field enhancement 211, in conjunction withany externally-supplied bias voltage 213, provides sufficient electricfield strength to barrier layer 502 to provide a means to induce flow ofelectric current 212. Barrier layer 502 is useful to enhance the ratioof the detected electric current 212 to the background electric currentand may influence the nonlinearity that produces the difference betweenforward current 214 and reverse current 215 that leads to net electriccurrent 212 The illustration represented in FIG. 5 is just one exampleof a bilayer structure that may be used to enhance the on/off ratio ofelectric current 212 relative to background and/or active layernonlinearity. Active layer 203 may comprise bilayer, trilayer, ormultilayer structures in various embodiments of the invention.Functionally, the active layer 203 may have the characteristics of oneor more of the following: semiconductor junctions, barrier junctions,Frenkel-Poole hopping layers, Fowler-Nordheim tunneling layers,field-emission layers, or ballistic carrier transport layers.

In a similar fashion to that illustrated in FIG. 5, FIG. 6 shows anembodiment of an integrated resonance detector 220 where active layer203 is composed of a composite mixture of two solid compounds. In thisexample, the majority, or “bulk” material 601 of active layer 203 couldbe a semi-insulator that supports zero or small dark current flow underexternal bias. A secondary component 602, such as semiconducting ormetallic nanoparticles, may be provided for supporting flow of electriccurrent 212 under applied bias 213 in conjunction with sufficient fieldenhancement 211. In one embodiment, applied bias 213 polarizes thecharge carriers on secondary component 602, but is not sufficient tolead to flow of net electric current 212 directly. When the opticalresonance conditions are met, i.e., when integrated resonance detector220 interacts with a specific wavelength of electromagnetic radiation asdetermined by resonance layer feature dimensions 205, electric current212 will flow between patterned conductor layer 204 and conductingmirror layer 202 through electrode terminals 216 and 217, to bequantified in external circuit 218. The mode of current flow may bevariable range hopping between individual particles of secondarycomponent 602 that are mixed with bulk material 601 in somepredetermined concentration. This condition would only occur when thecombination of the electric field supplied by applied bias 213 pluselectric field enhancement 211 is sufficient to enable charge carriersto overcome the potential barrier imposed between individual particlesof secondary component 602 in bulk material 601. Fabrication of anynumber of ratiometric mixtures of two solid components to achieve theoptimum nonlinear current-voltage characteristic are envisioned invarious embodiments of the invention, non-limiting examples ofratiometric mixtures include semiconductor nanoparticles such as indiumor tin oxide in a polymeric film, or conducting nanoparticles such asgold in a spin-on glass of silicon dioxide. Secondary component 602 andbulk material 601 may comprise ratiometric mixtures of conductors,semiconductors, semi-insulators, or insulators that form a compositeactive layer 203.

In some aspects of the invention, patterned conductor layer 204 iscomposed of parallel lines, or “grooves” forming a grating-likestructure. This pattern was illustrated previously in FIG. 2-6 inisometric view. In this embodiment, integrated resonance detector 220may respond to specific polarizations of electromagnetic radiation inaddition to specific wavelengths. The ability to interspersepolarization-dependent integrated resonance detectors of differentorientations into the distribution of wavelength-selective components isone of the compelling features of the invention. Spectro-polarization orpolarization images may be useful in applications such as surveillancewhere man-made objects are known to reflect polarized light differentlythan natural objects. An important feature of the groove, or “strip”structure is that a single, common bridging strip 209 that traverses allof the resonance lines can connect all the resonance lines to a commonelectrode terminal 217. Bridging strip 209 can be positioned so as notto interfere with the optical resonance and serves only to enableelectrical continuity between patterned features 205 of patternedconductor layer 204.

An alternative method to create electrical continuity between thepatterned features 205 of patterned conductor layer 204 is to leave athin continuous film 701 below the features, FIG. 7. Thin continuousfilm 701 is sufficiently thin so as to not interfere with opticalresonance, but is sufficient to carry current from patterned conductorlayer 204 to the external circuit in a similar fashion to bridging strip209. This method is amenable to all feature shapes including the set ofparallel lines shown in FIG. 2, or for example, a cross-hatch, or arrayof squares or pillars, hexagonal arrangements and other two dimensionalgeometries. Devices fabricated with cross-hatched patterned conductorlayers 204 may provide polarization-independent absorption, thusfunctioning solely as a wavelength-selective detector or detector array.

FIG. 8 shows a schematic representation of one example in whichintegrated resonance detector 220 is incorporated as a subcomponent atthe pixel level of a silicon CMOS image sensor 801 acting as substrate201. In the figure, four active silicon CMOS detection regions, or“pixels” are represented by 802A-D. Each pixel comprises a filter layer803, a photoactive area 804 and a detector circuit 805 that ismanufactured to be addressable by an external multiplexer and read-outamplifier circuit. In the embodiment depicted in FIG. 8, one of thesilicon CMOS sensor pixels 802D is replaced by an integrated resonancedetector 220D. FIG. 8 depicts patterned conductor layer 204 inregistration with a single pixel 802D in the detector array. One-to-oneregistration of integrated resonance detector 220 with underlyingdetector array pixel 802 is not required. Integrated resonance detector220D can be designed to selectively absorb SWIR or MWIR radiation, forexample, which would not otherwise be detected by silicon CMOS imagesensor photoactive areas 802A-C. Integrated resonance detector 220Dcould be interfaced to detector circuit 805D in the same manner pixels802A-C are interfaced to detector circuits 805A-C. This could beaccomplished during manufacturing or possibly included in a retrofitapplication of an existing CMOS image sensor. In either embodiment, theprinciple of increasing the wavelength range of detection by inclusionof integrated resonance detectors applies. Numerous embodiments existfor the arrangement of detector pixels 801 and integrated resonancedetectors 220 that would enable a monolithic UV, VIS, NIR, and SWIRdetector array.

FIG. 9 shows photograph 901 with specific examples of integratedresonance detectors 220. Photograph 901 illustrates multiple dies 902(total of fifty-two) on the wafer of large arrays 303 of integratedresonance detectors 220. In this example, large array 303 was fabricatedusing lithographic processing techniques. As part of the process,nanoscale patterning techniques such as nanoimprint lithography wereused to define the patterned features 205 in patterned conductor layer204. Nanoimprint-patterned conductor layer 204 appears bright in photoinset 903 due to diffraction of room lighting. When feature dimensions205 of patterned conductor layer 204 in integrated resonance detector220 are smaller than the wavelength of visible light, they appear darkin the photograph, for example in the region indicated by 904. Differentshadings (colors) are observed in photo inset 903 for different sizes ofpatterned features 205.

Scanning electron micrograph (SEM) 905 illustrates a specific example ofan integrated resonance detector 220. In this example, a silicon waferis used as substrate 201. Conducting mirror layer 202 is a trilayermetal stack consisting of chromium (1.5 nm)-gold (97 nm)-chromium (1.5nm). Chromium is used as an adhesion promoter, or tie layer for bondinggold to inorganic layers and is well known in the art. Active layer 203consists of a single indium oxide (In₂O₃) 100 nm thick layer. Activelayer deposition is followed by deposition of patterned conductor layer204 which, like the mirror layer, is composed of a chromium (1.5 nm) tielayer and a final 100 nm of gold. Nanoimprint lithography is employed tocreate the patterned features 205 in patterned conductor layer 204.Nanoimprint lithography provides a means to define features using aquartz template that has been defined using an electron beam lithographyprocessing step and is described by Sreenivasan et al. U.S. Pat. No.6,900,881, which is hereby incorporated by reference. Nanoimprintlithography can be used to stamp and repeat the entire die pattern 902during a single imprint processing step. This process enables an entirelarge array 303 of integrated resonance detectors to be fabricated in abatch step. In the example in FIG. 9, the feature width 206 is 230 nmand feature pitch 207 is 315 nm. The feature gap 906, defined as thewidth of the area that is voided of patterned conductor layer 204, is apronounced feature of SEM micrograph 905 in the specific example.Definition of patterned conductor layer 204 completes the formation ofresonance structure 219 which becomes integrated resonance detector 220(not shown) when connected to an external electric circuit.

FIG. 10 shows a plot of the absorption vs. wavelength measured with aninfrared (IR) spectrometer for a series of integrated resonancedetectors 220. The absorption curves demonstrate that for any specifiedpatterned feature dimensions 205, there exists a peak absorptionwavelength when the integrated resonance detector 220 is irradiated withlinearly-polarized radiation with an electric field orientation that isperpendicular to the long axis of patterned features 205. A second setof curves illustrates that no peak absorption occurs whenlinearly-polarized light is parallel to the long axis of patternedfeatures 205 of patterned conductor layer 204. For linearly-polarizedlight perpendicular to the long axis of patterned features 205, thewavelength of peak absorption changes when patterned feature dimensions205 of patterned conductor layer 204 are changed. Data graph 1001 showsboth sets of curves for each of the five different feature dimensions205 included in array die 902 for an example large array 303 ofintegrated resonance detectors 220. For the data set, the featuredimensions are defined as the feature width (W) 206 and feature pitch(L) 207. The five curves for linearly-polarized light perpendicular tothe long axis include line 1011 (L=300 nm, W=230 nm, λ_(max)=1.40 μm);line 1012 (L=315 nm, W=250 nm, λ_(max)=1.62 μm); line 1013 (L=330 nm,W=250 nm, λ_(max)=1.74 μm); line 1014 (L=450 nm, W=350 nm, λ_(max)=2.00μm); and line 1015 (L=450 nm, W=375 nm, λ_(max)=2.25 μm). Likewise, therespective curves for linearly-polarized light parallel to the long axisare line 1031 (L=300 nm, W=230 nm); line 1032 (L=315 nm, W=250 nm); line1033 (L=330 nm, W=250 nm); line 1034 (L=450 nm, W=350 nm); and line 1035(L=450 nm, W=375 nm), and are plotted over the same range ofwavelengths. However, absorption of linearly-polarized light parallel tothe long axis is low compared to perpendicular linearly-polarized lightindicating that the light is non-interacting with the resonancestructure 219. The absorption data are demonstrated without connectionto an external circuit 218. Connection of resonance structure 219 to anexternal circuit would produce integrated resonance detector 220. In theevent the devices are connected to an external circuit 218, analogouspeaks in electric current 212 vs. wavelength 209 curves would beobserved. The sharpness, or Q-factor for the absorption width and peakabsorption are dependent on a number of physical variables including thenumber of consecutive patterned conducting layers 204 that are depositedand patterned.

Another embodiment of a large array 303 of integrated resonancedetectors 220 is illustrated in FIG. 11. The composition of substrate201 consists of a metallized (aluminum) Kapton® film 1102 that is coatedwith a thin active layer (In₂O₃) 203 followed by deposition of theimprinted photoresist that is used to pattern patterned conducting layer204. In this example, large array 303 with individual integratedresonance detectors 220 are not connected to external circuits 218. Aswas demonstrated in FIG. 9, some of integrated resonance detectors 220appear as bright spots due to room light diffraction and others 904,have feature dimensions 205 that are too small to cause diffraction ofvisible light. Fabrication of integrated resonance detectors 220 ontoflexible substrates opens new manufacturing possibilities forphotodetector arrays that are not possible when rigid wafer substratesare employed. Numerous possibilities exist for flexible substrates andmaterial compositions that could comprise substrate 201.

Large arrays 303 of integrated resonance detectors 220 may be used in anumber of optical detection applications. One embodiment, such as thatdepicted previously in FIG. 8, is to enable near infrared and short waveinfrared detection with visible detection using a monolithic imagesensor as the substrate. In this embodiment, broad wavelength detectionwill not require secondary focal plane arrays such as InGaAs, InSb, orHgCdTe which have cost ratios>1000 times that of silicon detectors.Infrared focal plane arrays are manufactured for different regions ofthe infrared from near infrared (NIR) to long-wave infrared (LWIR).Infrared focal plane arrays are commercially available (e.g., Goodrich;Princeton, N.J., USA and FLIR Systems Inc.; Boston, Mass., USA).

In another embodiment, a silicon CMOS image sensor could be designed toinclude integrated resonance detectors 220 and the image sensor colorfilter array would be redesigned to accommodate the infrared “pixels”composed of integrated resonance detectors 220 via elimination of selectcolor filter elements and/or expansion of the traditional 2×2 Bayerfilter pattern for color analysis (U.S. Pat. No. 3,971,065). A Bayer CFAcomprises an alternating pattern composed of one red, two green, and oneblue filter, each in registration with a single image detector pixel.This type of pattern is referred to as a 2×2 pixel pattern, because thepattern has 4 pixels in a 2×2 arrangement.

In one embodiment disclosed herein, a silicon CMOS image sensor is madeto have a variety of CFA patterns including a 2×2 pixel pattern such asthat used by a Bayer color filter array that incorporates at least somefraction of integrated resonance detectors 220 in place of CFA elements.The degree of incorporation depends on the desired application.Embodiments can be conceived where only a single element is replaced toaccommodate infrared detection. Conversely, embodiments can be conceivedwhere all but one color element is incorporated in the infrared array.

In other aspects of the invention, image sensor arrays with at least oneintegrated resonance detector 220 are made to have 3×3 pixel patterns,4×4 pixel patterns, 5×5 pixel patterns and/or up to N×N pixel patterns,where N is limited by the number of electrically addressable pixels inthe array. In still other aspects of the invention, image sensor arrayswith at least one integrated resonance detector comprise one or moredifferent pixel patterns. Expanding the size of the pixel pattern from atypical 2×2 pattern to a 3×3, 4×4, 5×5, or higher pixel patterns enablesexpansion of a spectroscopic mosaic set beyond the standard RGB and CMYKpatterns currently used in visible filtering systems for cameras andother optics. The expanded mosaic may include any number of integratedresonance detectors 220 that absorb light in the NIR or SWIR regionsdesigned by changing the feature dimensions 205 of the patternedconductor layer 204. Furthermore, array dimensions may be asymmetric,for example a repeated 2×3, 2×4, 2×5, 2×7, 2×10, 2×17, 2×51, 2×200,2×1000, 3×4, 3×9, 3×300, 10×100 may be created. This can enable higherspectral definition, accommodate higher color fidelity, and can providefor the resolution of spectroscopically similar wavelengths ofultraviolet, visible and infrared radiation in applications such ascombined photography and thermography and laser threat detectionidentification, to name a few. Array dimensions need not be square, orrectangular and may take the form of any repeatable geometric shape.

An array of integrated resonance detectors may also be fabricated on asubstrate that contains electric circuits, for the purposes ofamplifying, digitizing, or otherwise converting the currents from thearray of integrated resonance detectors into electrical signals. In somecases, it is useful for the substrate electric circuits to be connectedto a combination of photodetectors with spectral responses inherent tothe materials comprising the photodetectors, and integrated resonancedetectors provided in the present invention. For example, it may beadvantageous to provide an array of integrated resonance detectors withdimensions designed to detect radiation in the mid-wave infrared band,on a substrate that contains an array of silicon photodetectors, whichare primarily sensitive to radiation in the visible and near-infraredbands. The combination of detection capability across the visible,near-infrared, and mid-wave infrared bands afforded by a single devicethat combines certain embodiments of the present invention withconventional photodetectors known in the art solves a difficult problemof utility in the formation of spectrally-resolved imaging of scenes. Asa particular, non-limiting example, an array of integrated resonancedetectors of the present invention, with dimensions designed to providedetection of radiation in a number of wavelength intervals across theshort-wavelength infrared band (0.9 μm-2.1 μm), fabricated on a siliconphotodetector array with a Bayer filter mosaic (RGB) and electronicamplification circuitry for both the individual silicon photodetectorsand the individual integrated resonance detectors, can be used as afocal-plane detector for a hyperspectral imaging system.

In the present invention, instances where the integrated resonancedetectors are combined with photodetectors may include a color filterarray as part of the system. The color filter mosaic may be present onlyon the photodetector elements, or it may be included on both thephotodetector elements and on the integrated resonance detectors. In thecase where the color filter element is deposited on an integratedresonance detector, the layer would serve to pre-filter light to aspecific spectroscopic region which would then be furtherspectroscopically narrowed by virtue of the resonance interaction withthe incident light. This may be useful, for example, in backgroundrejection or enhancing the dynamic range of detection for specificimaging applications or laser threat detection.

An integrated resonance detector array may contain many regions ofwavelength selectivity. In various aspects of the invention, groupingsof detection pixels may occur to increase the wavelength spectral range,the dynamic range of detection, or the sensitivity of the response for agiven narrow range of wavelengths. An example of narrow wavelengthselectivity would be wavelength division multiplexing. In otherembodiments of the invention, detector array 303 provides for a broaddetection capability ranging from the ultraviolet through far infraredregion of the electromagnetic spectrum. In other embodiments, selectedbroad ranges of wavelengths may be used for solar radiation detection,energy conversion or collection. The integrated resonance detector arrayof the present invention would provide for both a monolithic detectorarray or an arrangement of individual sensor elements in an array, eachembodiment possessing a mosaic of individual detector elements specificto a given wavelength of resonance coupling. Broad wavelength detectorarrays capable of spanning a large spectroscopic range as a monolithicdetector (i.e., not requiring stitching of multiple detection systemsfrom visible to far infrared) are not known in the art.

In some embodiments, the resonance structure in an integrated resonancedetector can be designed specifically to retain its wavelength-selectivecharacteristics over a broad range of incident angles. This featureprovides an advantage over some other methods of wavelength selectivityused in the art. For example, thin-film interference or Fabry-Perotfilters have narrow angular acceptance for a given center selectedwavelength (S.-W. Han, et al. “Multilayer Fabry-Perot microbolometersfor infrared detection” Infrared and Millimeter Waves and 13thInternational Conference on Terahertz Electronics, 2, p. 646, 2005).Wide angle selectivity of the integrated resonance structures has beendemonstrated in the literature (Avitzour, Y. et al., “Wide-angleinfrared absorber based on a negative-index plasmonic metamaterial”Phys. Rev. B 79(4) p. 045131, 2009 and Chihhui, W. et al., “Ultra-thinwide-angle perfect absorber for infrared frequencies” SPIE—The Intl.Soc. For Optical Eng. 7029, p. 70290W-7015, 2010).

Several specific applications are enabled by embodiments of theinvention including electromagnetic sensor arrays, energy collectionsuch as solar energy, and logic circuits that can spatially andspectrally resolve incident light by virtue of fabricating a largenumber of detectors, each detector having feature dimensions tailored tobe resonant within a narrow, but different band of wavelengths. Such adevice architecture could be useful, for example, in the fabrication ofa hyperspectral detector that is used as a focal plane array in animaging system, spectral encoding of optical logic circuitry thatprovides a means for dense logic element packaging, and wavelengthdivision multiplexing of narrow optical communication bands.Furthermore, the material composition of the device could be selectedfor high temperature operation, making possible applications such asthermophotovoltaic energy conversion.

It is understood that modifications to the invention may be made asmight occur to one skilled in the field of the invention within thescope of the appended claims. All embodiments contemplated hereunderwhich achieve the objects of the invention have not been shown incomplete detail. Other embodiments may be developed without departingfrom the spirit of the invention or from the scope of the appendedclaims. Although the present invention has been described with respectto specific details, it is not intended that such details should beregarded as limitations on the scope of the invention, except to theextent that they are included in the accompanying claims.

1. A method for making an integrated resonance detector forelectromagnetic radiation, comprising: (a) providing a substratecomprising a conducting mirror layer, the mirror layer having electricalcontinuity to a first electrode; (b) depositing an active layer on themirror layer; (c) depositing a conducting layer on the active layer, theconducting layer having electrical continuity to a second electrode; (d)patterning the conducting layer, wherein the patterned conducting layeris selected to absorb electromagnetic radiation within a selected rangeof wavelengths; and (e) connecting an electrical circuit between thefirst electrode and the second electrode.
 2. A method for making anintegrated resonance detector for electromagnetic radiation, comprising:(a) providing a substrate comprising a conducting mirror layer, themirror layer having electrical continuity to a first electrode; (b)depositing an active layer on the mirror layer; (c) patterning theactive layer; (d) depositing a conducting layer on the patterned activelayer, the conducting layer having electrical continuity to a secondelectrode and defining a specific wavelength of absorption; and (e)connecting an electrical circuit between the first electrode and thesecond electrode.
 3. The method of claim 1 wherein the conducting layeris patterned by dry etching.
 4. The method of claim 1 wherein theconducting layer is patterned with a liftoff process.
 5. The method ofclaim 1 wherein the active layer is deposited using evaporation,sputtering, chemical vapor deposition, spin-on, or casting.
 6. Themethod of claim 1 further comprising depositing a second active layer onthe patterned conductive layer.
 7. The method of claim 6 furthercomprising depositing a second patterned conducting layer on and inregistration with the second active layer.
 8. The method of claim 1wherein the conducting layer is patterned by photolithography ornanoimprint lithography.
 9. The method of claim 1 wherein the electricalcircuit comprises a focal plane array, image sensor, or bolometer. 10.The method of claim 2 wherein the active layer is deposited usingevaporation, sputtering, chemical vapor deposition, spin-on, or casting.11. The method of claim 2 further comprising depositing a second activelayer on the patterned conductive layer.